1. Field of the Invention
The present invention relates to a small watercraft such as a personal watercraft (PWC) which ejects water rearward and planes on a water surface as the resulting reaction. More particularly, the present invention relates to a cooling system of an engine or the like of the small watercraft.
2. Description of the Related Art
In recent years, so-called jet-propulsion personal watercraft, which are one type of small watercraft, have been widely used in leisure, sport, rescue activities, and the like. The jet-propulsion personal watercraft is configured to have a water jet pump that pressurizes and accelerates water sucked from a water intake generally provided on a bottom surface of a hull and ejects it rearward from an outlet port. Thereby, the personal watercraft is propelled.
In the jet-propulsion personal watercraft, a steering nozzle provided behind the outlet port of the water jet pump is swung either to the right or to the left by operating a bar-type steering handle to the right or to the left, to change the ejection direction of the water to the right or to the left, thereby turning the watercraft to the right or to the left.
In propulsion engines of small watercraft, including the jet-propulsion personal watercraft, a temperature and temperature distribution of various portions of the engine vary. This causes deformation of the engine and thereby degrades engine performance, or the like. Due to deformation of the engine, a clearance between an inner wall of a cylinder and a piston varies and friction between them thereby increases. In addition, a gasoline adhering to the inner wall of the cylinder without being vaporized moves into a crankcase and reduces the concentration of oil in the crankcase. In particular, in the case of an engine designed to minimize clearance between the piston and the cylinder for the purpose of reducing lubricating oil consumption or a piston lap noise, the increase in friction is problematic.
The present invention addresses the above-described condition, and an object of the present invention is to provide a small watercraft having an engine cooling system which can lessen a temperature distribution of an engine.
According to the present invention, there is provided a small watercraft comprising an engine for driving a propulsion unit of the watercraft, the engine including a first cooling passage formed inside a cylinder head of the engine, for cooling the cylinder head with a coolant flowing therethrough; and a second cooling passage formed inside a cylinder block of the engine, for cooling the cylinder block of the engine with a coolant flowing therethrough, the first and second cooling passages being independent of each other.
In accordance with the small watercraft having the above-described engine cooling system, since the coolant is independently supplied to the first cooling passage for supplying the coolant to the cylinder head of the engine and to the second cooling passage for supplying the coolant to the cylinder block of the engine, a large amount of coolant can be supplied to the cylinder head that generates more heat and a small amount of coolant can be supplied to the cylinder block that generates less heat. In addition, a low-temperature coolant can be supplied to the cylinder head and a coolant which has been used for cooling another component and has a temperature higher than that of the coolant of the first cooling passage can be supplied to the cylinder block. This allows a temperature distribution of the cylinder head and the cylinder block of the engine to be made uniform.
Preferably, the amount of the coolant flowing through the first cooling passage may be more than the amount flowing through the second cooling passage. This allows a temperature distribution in the engine to be made uniform.
Preferably, the small watercraft may further comprise a first cooling water supply pipe for supplying the coolant to the first cooling passage; and a second cooling water supply pipe for supplying the coolant to the second cooling passage.
Preferably, a flow cross-sectional area of the second cooling water supply pipe may be smaller than a flow cross-sectional area of the first cooling water supply pipe. In this structure, the amount of the coolant to be supplied to the cylinder block of the engine is less than the amount of the coolant to be supplied to the cylinder head, regardless of the amount of the coolant supplied to the cylinder head. This allows a temperature distribution in the engine to be made uniform. Because of the lesser amount of coolant, the cylinder block of the engine smoothly and quickly increases its temperature during the start of the engine. As a result, a clearance between an inner wall of the cylinder and a piston is rendered in a proper condition in a short time when the engine is starting.
Preferably, the flow cross-sectional area of the second cooling water supply pipe may be half as small as the flow cross-sectional area of the first cooling water supply pipe.
Preferably, the small watercraft may further comprise an exhaust pipe attached to an exhaust port of the engine, the exhaust pipe having a water jacket through which the coolant is supplied to the second cooling passage. Thereby, the coolant, which has passed through the exhaust pipe and has an increased temperature higher than a temperature of the coolant supplied to the cylinder head, is supplied to the cylinder block, and the temperature distribution of the engine can be made uniform.
In this structure, preferably, the coolant may be supplied to the first cooling passage through a first cooling water supply pipe and the coolant may be supplied to the second cooling passage through a second cooling water supply pipe connected to the water jacket of the exhaust pipe, wherein a flow cross-sectional area of the first cooling water supply pipe may be substantially equal to a flow cross-sectional area of the second cooling water supply pipe.
Preferably, water outside the watercraft may be supplied to the first and second cooling passages as the coolant. Since plenty of low-temperature water is supplied as the coolant, the small watercraft can have a sufficient cooling capability while in an operating state with a large load.
Preferably, the first cooling passage and a first cooling water supply pipe may form a first closed loop within which the coolant circulates, and the second cooling passage and a second cooling water supply pipe may form a second closed loop within which the coolant circulates. This structure prevents entry of unwanted substances into the first and second cooling passages.
In this structure, preferably, a flow cross-sectional area of the second cooling water supply pipe may be smaller than a flow cross-sectional area of the first cooling water supply pipe. The amount of the coolant to be supplied to the cylinder block of the engine that generates less heat is less than the amount of the coolant to be supplied to the cylinder head regardless of the amount of coolant supplied to the cylinder head. This allows the temperature distribution in the engine to be made uniform.
Preferably, the flow cross-sectional area of the second cooling water supply pipe may be substantially half as small as the flow cross-sectional area of the first cooling water supply pipe.
Preferably, the small watercraft may further comprise a cooler provided in the first and second closed loops, for cooling the coolant flowing within the first and second closed loops, the cooler being adapted to cool the coolant flowing within the closed loops with water drawn from outside the watercraft to the cooler. Thereby, effective indirect cooling of the engine is achieved with a simple structure.
The above and further objects and features of the invention will be more fully be apparent from the following detailed description with the accompanying drawings.